Sliding mode control of electro-hydraulic servo system based on ESO fuzzy switching gain adjustment

Electro-hydraulic force servo systems are widely applied in aerospace, aviation, industrial automation, and manufacturing due to their advantages of high power-to-volume ratio, large stiffness, and fast response speed. However, the intrinsic nonlinearities, model and parameter uncertainties, as well as the ubiquitous external disturbances under operating conditions, significantly affect their performance, making it difficult for conventional control methods to fully meet the dynamic and static performance requirements. To address this issue, this paper establishes a state-space model incorporating system stiffness and external disturbances, and designs an Extended State Observer (ESO) to simultaneously estimate the output force, the force variation rate, and the lumped disturbance. On this basis, a Fuzzy-Switched-Gain Sliding Mode Control (FSG-SMC) strategy is proposed, in which fuzzy rules constructed from the tracking error and sliding surface are employed to adaptively adjust the gain of the reaching law online, thereby achieving a trade-off between disturbance rejection and chattering suppression. Lyapunov analysis is provided to guarantee the closed-loop stability. The proposed method is validated through co-simulation using Simulink and AMESim, as well as experiments on an electro-hydraulic force servo test rig. Results demonstrate that under sinusoidal inputs from 1 to 20 Hz, the system satisfies the “double-ten” criterion (amplitude attenuation < 10%, phase lag < 10°); the step response exhibits no overshoot with a settling time of approximately 0.002 s; the relative error between simulation and experiment is within 10%, and the steady-state error is about 200 N. Moreover, the proposed controller significantly suppresses chattering under high-frequency conditions. These results confirm that the method enhances robustness while maintaining fast response and engineering feasibility.